The development of hydrogen and/or deuterium generation sources for fuels for lasers has obviated the need for high pressure storage facilities under cryogenic conditions.
After the development of hydrogen and/or deuterium generation sources for high purity laser fuels the needs were recognized for additional improvements such as chemical reactants capable of generating hydrogen or deuterium in higher yield and with higher purity as evidenced by the evolution of the art described below.
A comprising a cured intimate mixture of about 85% to 95% by weight hydrazine bisborane and about 5% to 15% by weight of an organic polymeric binder is disclosed in U.S. Pat. No. 3,170,283 by David C. Sayles. This composition decomposes to yield decomposition products of hydrazine bisborane consisting of H.sub.2 and B.sub.3 N.sub.3.
Compositions which generate hydrogen are disclosed in U.S. Pat. No. 3,666,672, "Hydrogen Generating Compositions", by Ralph H. Hiltz. Disclosed is an autogeneously combustible composition that liberates hydrogen on burning. The composition contains an alkali metal borohydride and hydrazine sulfate in proportions such that there are between about 0.5 to 2 boron atoms for each nitrogen atom.
Examples of prior art compositions for producing hydrogen or deuterium at about 600.degree. C.-700.degree. C. are disclosed by Ayers et al in U.S. Pat. No. 3,948,699. These compositions are based on complex metal boron compounds of the general formula M(BH.sub.4).sub.x or M(BD.sub.4).sub.x' (wherein M equals a metal and x equals the valence of the metal M; M is an alkali metal or an alkali earth metal; H is hydrogen, and D is deuterium) and metal oxides of the general formula Q.sub.2 O.sub.3 (wherein Q is a trivalent metal selected from iron, aluminum, gallium, cobalt, and indium) combined stoichiometrically.
Higher temperature hydrogen or deuterium (e.g., about 3000.degree. C.) production is disclosed by Ayers et al in U.S. Pat. No. 3,948,700. This patent discloses a storable solid propellant composition based on unsolvated aluminum deuteride or unsolvated aluminum hydride and ferric oxide which produces high temperature gases from a self-sustaining reaction, once started, by a heat source such as an electrically heated nickel-chromium ignition wire. The hydrogen or deuterium produced is acceptable for use in HF/DF and HCl chemical lasers, the gas dynamic laser (GDL), or a source of hot gases for reducing fuel.
Channell et al discloses in U.S. Pat. No. 4,021,362 a gas generating system for chemical lasers which comprises a solid composition comprised of about 60 to 70 percent by weight of lithium aluminum deuteride, about 20 to 30 percent of deuteroammonium chloride, about 5 to 15 percent by weight iron oxide, and about 3 to 4 percent by weight of a hydrocarbon polymeric binder.
Additional prior art is disclosed by Chew et al in U.S. Pat. Nos. 4,061,512 and 4,064,225 which relate to storable solid propellent compositions and method of producing hydrogen or deuterium from these complex metal boron compounds of the general formula M(BH.sub.4).sub.x or M(BD.sub.4).sub.x (wherein M equals a metal and x equals the valence of the metal M; M is an alkali metal or an alkaline earth metal; H is hydrogen, and D is deuterium) and ammonium salts of the general formula (NH.sub.4).sub.n Y or deuteroammonium salts of the general formula (ND.sub.4).sub.n Y (wherein Y represents an anion with a total charge of n; N is nitrogen, H is hydrogen, and D is deuterium). The specified compounds combined stoichiometrically or in varying molar ratios produce hydrogen or deuterium that contains nitrogen as an inert diluent which is acceptable for use in HF/DF chemical lasers, the gas dynamic laser GDL, or as a source of hydrogen containing an inert duluent.
In recent disclosures by Chew et al in U.S. Pat. No. 4,157,927, a class of compounds known as amine-boranes and their derivatives are mixed with heat producing compounds such as lithium aluminum hydride or a mixture, such as NaBH.sub.4 /Fe.sub.2 O.sub.3 mixtures combined in definite proportions in a mixer or ball mill to produce a uniformly mixed powder. The mixed powder is then pressed into pellets and ignited to produce the hydrogen or deuterium as well as by products that are non-deactivating diluents. The oxide/borohydride or oxide/aluminohydride combination provides the thermal energy for decomposition of the amine borane.
Joseph E. Flannagan discloses in U.S. Pat. No. 4,166,843 a solid propellant gas generator system employing borane compounds of the formula (CH.sub.3).sub.x H.sub.4-x NB.sub.3 H.sub.8 as the primary source and a metallic complexing agent to trap the carbon molecules as solid metallic carbides.
The review of extensive prior art from 1965 through 1979 has revealed several approaches which have been investigated as possible means of developing storable sources of H.sub.2 and D.sub.2. The systems that have been studied are primarily based on complex borohydrides, or aluminohydrides, and ammonium salts. These systems have an upper theoretical weight yield (H.sub.2) limit of approximately 8.5%. Recent systems studies have indicated that an improvement in the H.sub.2 weight yield is desirable and the systems under discussion provide the desired theoretical performance.
The required improvements in H.sub.2 (D.sub.2) weight yield will not result from solid reactants based upon the interaction of metal borohydrides, or aluminohydrides, and ammonium salts, or from catalytic decomposition of the active hydride compounds. This pessimistic viewpoint is based on the fact that for the NaBH.sub.4 /NH.sub.4.sup.+ salt systems, for example, the generation of hydrogen is the result of the reaction of the NH.sub.4.sup.+ cation and the BH.sub.4.sup.- anion. Therefore, the counter ions only serve to stabilize these reactive ions and, consequently, result in a lower gas weight yield because of their additional weight.
Because of this drawback of current solid reactants for H.sub.2 (D.sub.2) generation, the approach to be used for achieving higher weight yields is to consider those compounds that have, on a molecular basis, only those chemical groups that react to form H.sub.2 (D.sub.2. Such compounds exist and should provide the desired improvements in gas yield provided the proper combination is discovered.
Representative of the classes of compounds considered for this application and which contain only B, N, and H (both positive and negative) are:
1. Amine boranes (AB); PA1 2. Boron hydride ammoniates (DDA); PA1 3. Borazanes (HBB); and, PA1 4. Ammonium octahydrotriborates or tetrahydroborates
Compounds within the first three general classes, although both positive and negative hydrogens are present, are thermally stable and vary in their hydrolytic stability. while quarternary alkyl ammonium octahydrotriborates and tetrahydroborates are thermally stable, the unsubstituted ammonium salts readily decompose at or below ambient temperature.
The only hydrogen generator compound, of the three primary candidates presented under 1, 2 and 3 above which has self sustaining combustion characteristics is HBB. Unfortunately, this compound tends to go through a deflagration to detonation transition (DDT) rather easily. Combinations of HBB and AB-1, wherein the HBB concentration is greater than 30 weight percent, also tend toward DDT. Insufficient heat generation from the hydrogen generator formulation results in poor ignition and incomplete decomposition of the primary hydrogen containing molecule. The rationale for this thermal decomposition process is presented in the following equations. ##STR1## Decomposition of AB-1 is a step-wise reaction as shown in equations (1) through (4) and is quite slow and incomplete unless sustained high temperatures are available.
Therefore, a primary object of this invention is to provide a primary source in the form of hydrogen or deuterium generator molecule in combination with other heat sources to aid in decomposition of the primary source for hydrogen or deuterium generation.
Another object of this invention is to provide a gas generator composition which produces a high yield of greater than 15 weight percent hydrogen having a purity greater than 98 mole percent of hydrogen.
A further object of this invention is to provide a gas generator composition which decomposes efficiently without going through a deflagration to detonation transition (DDT).